Why Brad Pitt decided to go to Jennifer Aniston's birthday party (exclusive)

Amicable exes is a bit of an understatement when it comes to Brad Pitt and Jennifer Aniston!

The former spouses were reunited over the weekend, when Pitt attended Aniston’s 50th birthday party at the Sunset Tower in Los Angeles, California. 

A source tells ET that Pitt “wanted to support” Aniston because the former couple have “been friendly” in the years following their split. 

According to the source, Aniston put her ex-husband on her invite list weeks ago and Pitt was in town and happily chose to attend to help her celebrate the milestone birthday.

Though he was at the party, Pitt and Aniston didn’t have much interaction at the event. They were, however, seen briefly talking and exchanging a hug. The source adds that Pitt did not stay at the bash the entire night. 

“He came to support her, spoke to other friends of his that were there and headed out,” the source notes. 

23 PHOTOS
Jennifer Aniston and Brad Pitt together
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Jennifer Aniston and Brad Pitt together
LOS ANGELES - SEPTEMBER 12: Actor Brad Pitt and actress Jennifer Aniston attend the 51st Annual Primetime Emmy Awards on September 12, 1999 at Shrine Auditorium in Los Angeles, California. (Photo by Ron Galella, Ltd./WireImage)
Brad Pitt and Jennifer Aniston (Photo by Barry King/WireImage)
Jennifer Aniston and Brad Pitt shopping in Los Angeles, CA. November 23, 1999
UNITED STATES - circa 2000: Actress Jennifer Aniston with actor Brad Pitt. (Photo by The LIFE Picture Collection/Getty Images)
Jennifer Aniston and Brad Pitt (Photo by Jim Smeal/WireImage)
371747 01: Brad Pitt & Jennifer Aniston attending the Los Angeles Premiere of the new movie 'Erin Brockovich'. Westwood, California. March 14,2000. (Photo by: Brenda Chase Online USA Inc./Liaison Agency)
LOS ANGELES, CA - SEPTEMBER 10: Actor Brad Pitt and wife actress Jennifer Aniston arrive at the 52nd 2000 Primetime Emmy Awards on September 10, 2000 at the Shrine Auditorium in Los Angeles, California. (Photo by Ron Davis/Getty Images)
Brad Pitt and Jennifer Aniston at the premiere of 'The Mexican' at the National Theater in Los Angeles, Ca. 2/23/01. (Photo by Kevin Winter/Getty Images).
Brad Pitt and Jennifer Aniston during 'Rock Star' Los Angeles Premiere at Mann Village in Westwood, California, United States. (Photo by SGranitz/WireImage)
Jennifer Aniston & Brad Pitt during Spy Game Premiere at Mann National Theatre in Westwood, California, United States. (Photo by SGranitz/WireImage)
Jennifer Aniston and Brad Pitt arrive for the Golden Globe Awards at the Beverly Hilton Hotel in Beverly Hills, California January 20, 2002. (Photo by KMazur/WireImage)
Brad Pitt and Jennifer Aniston at the premiere of 'The Bourne Identity' at Universal CityWalk in Los Angeles, Ca. Thursday, June 6, 2002. Photo by Kevin Winter/ImageDirect
Jennifer Aniston and Brad Pitt arriving at the 54th Annual Prime Time Emmys. (Photo by Frank Trapper/Corbis via Getty Images)
UNITED STATES - JANUARY 12: Jennifer Aniston and Brad Pitt attending the premiere of 'Along Came Polly' at Grauman's Chinese Theater in Hollywood, CA 01/12/03 (Photo by Vinnie Zuffante/Getty Images)
SANTA MONICA, CA - MARCH 22: Actors Jennifer Aniston and husband Brad Pitt attend the 2003 IFP Independent Spirit Awards on March 22, 2003 in Santa Monica, California. (Photo by Jon Kopaloff/Getty Images)
Courteney Cox, Jennifer Aniston & Brad Pitt (Photo by Steve Granitz Archive 1/WireImage)
Brad Pitt and Jennifer Aniston at the Zeigfeld Theater in New York City, New York (Photo by Kevin Mazur/WireImage)
Brad Pitt, Jennifer Aniston during Warner Bros. Premiere of 'Troy' in New York City at Ziegfeld Theater in New York, New York, United States. (Photo by Sylvain Gaboury/FilmMagic)
CANNES, FRANCE - MAY 13: Actors Brad Pitt and Jennifer Aniston attend the World Premiere of epic movie 'Troy' at Le Palais de Festival on May 13, 2004 in Cannes, France. Aniston wears a dress by Versace. (Photo by Dave Hogan/Getty Images)
CANNES, France: US actor Brad Pitt and his wife Jennifer Aniston arrive for the official projection of US director Wolfgang Petersen's film 'Troy' , 13 May 2004, at the 57th Cannes Film Festival in the French Riviera town. Hollywood took over the French Riviera today as Brad Pitt and his co-stars of the epic movie arrived to present their 175 million dollar (147 million euro)-plus swords-and-sandals feature, being shown out of competition, in the blaze of Cannes publicity. AFP PHOTO/FRANCOIS GUILLOT (Photo credit should read FRANCOIS GUILLOT/AFP/Getty Images)
Actors Brad Pitt and Jennifer Aniston attend the premiere of Petersen's movie 'Troy', at the 57th Cannes film festival. (Photo by Stephane Cardinale/Corbis via Getty Images)
Jennifer Aniston and Brad Pitt at the The Shrine Auditorium in Los Angeles, California (Photo by Gregg DeGuire/WireImage)
Brad Pitt and Jennifer Aniston during The 56th Annual Primetime Emmy Awards - Audience at The Shrine Auditorium in Los Angeles, California, United States. ***Exclusive*** (Photo by Jeff Kravitz/FilmMagic)
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The father of six went to great lengths not to be seen leaving the party, and hotel staffers and security helped make it difficult for him to be photographed.

Pitt and Aniston were married from 2000 to 2005. Not long after their breakup, Pitt started dating Angelina Jolie and years later, they were married.

A source told ET last February that Pitt and Aniston do stay in touch after they both split from their spouses, Aniston from Justin Theroux and Pitt from Jolie. 

“They have each other’s cell phone number and communicate from time to time," the source said. "This is nothing new. Jen and [Brad] have remained friendly."

As for just how friendly these exes are, a source told ET after Aniston called it quits with Theroux that the actress and Pitt were “absolutely not dating.” 

In addition to the 55-year-old actor being at Aniston's birthday party, other celebs in attendance included Katy Perry, Orlando Bloom, George and Amal Clooney, Robert Downey Jr., Jason Bateman, and Pitt’s ex-fiancee, Gwyneth Paltrow. 

20 PHOTOS
Jennifer Aniston out and about
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Jennifer Aniston out and about
LOS ANGELES, CA - OCTOBER 22: Jennifer Aniston attends the 2018 InStyle Awards at The Getty Center on October 22, 2018 in Los Angeles, California. (Photo by Rich Fury/Getty Images)
LOS ANGELES, CA - OCTOBER 22: Jennifer Aniston attends the 2018 InStyle Awards at The Getty Center on October 22, 2018 in Los Angeles, California. (Photo by Rich Fury/Getty Images)
LOS ANGELES, CA - OCTOBER 22: Jennifer Aniston arrives at the 2018 InStyle Awards at The Getty Center on October 22, 2018 in Los Angeles, California. (Photo by Steve Granitz/WireImage)
LOS ANGELES, CA - SEPTEMBER 15: Jennifer Aniston and Netflix Chief Content Officer Ted Sarandos attend Ted Sarandos' 2018 Annual Netflix Emmy Nominee Toast on September 15, 2018 in Los Angeles, California. (Photo by Emma McIntyre/Getty Images for Netflix)
COMO, ITALY - JULY 30: Jennifer Aniston is seen on set filming 'Murder Mystery' on July 30, 2018 in Como, Italy. (Photo by Emilio Andreoli/GC Images)
HOLLYWOOD, CA - JUNE 07: Actress Jennifer Aniston arrives at the American Film Institute's 46th Life Achievement Award Gala Tribute to George Clooney on June 7, 2018 in Hollywood, California. (Photo by Axelle/Bauer-Griffin/FilmMagic)
HOLLYWOOD, CA - JUNE 07: Jennifer Aniston attends 46th AFI Life Achievement Award Gala Tribute on June 7, 2018 in Hollywood, California. (Photo by Presley Ann/Patrick McMullan via Getty Images)
HOLLYWOOD, CA - JUNE 07: Courteney Cox (L) and Jennifer Aniston speak onstage during the American Film Institute's 46th Life Achievement Award Gala Tribute to George Clooney at Dolby Theatre on June 7, 2018 in Hollywood, California. 288523 (Photo by Kevin Mazur/Getty Images for Turner)
MALIBU, CA - JUNE 02: Jennifer Aniston attends the CHANEL Dinner Celebrating Our Majestic Oceans, A Benefit For NRDC on June 2, 2018 in Malibu, California. (Photo by Rich Fury/Getty Images)
MALIBU, CA - JUNE 02: Jennifer Aniston (L) and Courtney Cox attend the CHANEL Dinner Celebrating Our Majestic Oceans, A Benefit For NRDC on June 2, 2018 in Malibu, California. (Photo by Rich Fury/Getty Images)
INGLEWOOD, CA - APRIL 19: Actress Jennifer Aniston attends WE Day California at The Forum on April 19, 2018 in Inglewood, California. (Photo by Axelle/Bauer-Griffin/FilmMagic)
Actress Jennifer Aniston speaks on stage at the WE Day California at The Forum, in Inglewood, California, on April 19, 2018. (Photo by VALERIE MACON / AFP) (Photo credit should read VALERIE MACON/AFP/Getty Images)
BEVERLY HILLS, CA - JANUARY 07: In this handout photo provided by Netflix, Jennifer Aniston and Netflix Chief Content Officer, Ted Sarandos attend the Netflix Golden Globes after party at Waldorf Astoria Beverly Hills on January 7, 2018 in Beverly Hills, California. (Photo by Netflix via Getty Images)
BEVERLY HILLS, CA - JANUARY 07: In this handout photo provided by NBCUniversal, Presenters Carol Burnett and Jennifer Aniston onstage during the 75th Annual Golden Globe Awards at The Beverly Hilton Hotel on January 7, 2018 in Beverly Hills, California. (Photo by Paul Drinkwater/NBCUniversal via Getty Images)
WEST HOLLYWOOD, CA - DECEMBER 07: Jennifer Meyer and Jennifer Aniston attend Gilt.com, Jennifer Meyer & Jenna Dewan Tatum Launch Exclusive Jewelry Collection Benefitting Baby2Baby at Sunset Tower Hotel on December 7, 2017 in West Hollywood, California. (Photo by Stefanie Keenan/Getty Images for Gilt.com)
JIMMY KIMMEL LIVE! - ABCs Jimmy Kimmel Live! features a week of guest hosts filling in for Jimmy, starting Monday, December 4. The guest host for Thursday, December 7 was Melissa McCarthy with guests Octavia Spencer ('The Shape of Water'), Actor Dave Franco ('The Disaster Artist') and musical guest Hanson. (Randy Holmes/ABC via Getty Images) JENNIFER ANISTON, MELISSA MCCARTHY
HOLLYWOOD, CA - JULY 26: Actress Jennifer Aniston attends the ceremony honoring Jason Bateman with Star on the Hollywood Walk of Fame on July 26, 2017 in Hollywood, California. (Photo by Axelle/Bauer-Griffin/FilmMagic)
HOLLYWOOD, CA - JULY 26: Will Arnett and Jennifer Aniston attend the ceremony honoring Jason Bateman with Star On The Hollywood Walk Of Fame on July 25, 2017 in Hollywood, California. (Photo by JB Lacroix/WireImage)
HOLLYWOOD, CA - JULY 26: Jennifer Aniston and Justin Theroux attend the ceremony honoring Jason Bateman with a Star on The Hollywood Walk of Fame held on July 26, 2017 in Hollywood, California. (Photo by Michael Tran/FilmMagic)
BEVERLY HILLS, CA - FEBRUARY 26: Jennifer Aniston attends the 2017 Vanity Fair Oscar Party hosted by Graydon Carter at Wallis Annenberg Center for the Performing Arts on February 26, 2017 in Beverly Hills, California. (Photo by JB Lacroix/WireImage)
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